Six-time champion Serena reached her 10th semi-final at the All England Club with a 6-4, 6-4 win over Russia 21st seed Anastasia Pavlyuchenkova.
She goes on to face Russian world number 50 Elena Vesnina on Thursday for a place in the final.
Five-time champion Venus, seeded eight, enjoyed a 7-6 (7/5), 6-2 victory over Kazakhstan's world number 96 Yaroslava Shvedova to reach her first Wimbledon semi-final in seven years.
The 36-year-old will now face German fourth seed and Australian Open champion Angelique Kerber who reached her second Wimbledon semi-final with a 7-5, 7-6 (7/2) win over Simona Halep, the fifth seed from Romania.
Vesnina made her first semi-final at a major, by seeing off bride-to-be Cibulkova, the Slovak 19th seed, 6-2, 6-2.
"They showed Venus's score on court and I was like 'yaaaay'. I want her to win so bad, but not in the final if I'm there," said defending champion Serena, who took her grand slam match win record to 302 - four behind Martina Navratilova's all-time mark.
It is the 11th time that the sisters have advanced to the semi-finals of the same major event.
Venus is the oldest women's semi-finalist since Martina Navratilova in 1994.
Venus, who won the last of her seven major titles at Wimbledon in 2008, is back in the last-four of a grand slam for the first time since the 2010 US Open.
The eight-time Wimbledon finalist trails 3-2 in her five career meetings with 28-year-old Kerber, who won their only meeting on grass in the 2012 Olympics at Wimbledon.
"I love playing the game. When you are winning matches it makes it that much sweeter," the German said.
"You can't always have these big moments. I guess if you are Serena Williams it happens a lot, but for Venus Williams this is an awesome day."
Kerber now has 33 match wins in 2016, joint-best with Cibulkova.
Cibulkova is due to marry fiance Miso Navara in her hometown of Bratislava on Saturday - the same day as the women's final - and the 27-year-old was willing to postpone the ceremony if she won her quarter-final.
But 29-year-old Vesnina took advantage of a distracted display from Cibulkova to become the fifth unseeded woman to reach the All England Club semi-finals since the Grand Slams switched to 32 seeds in 2001.